Refrigeration apparatus

ABSTRACT

A refrigeration apparatus includes: a usage-side expansion valve whose opening degree is changed in response to a change in a flow rate or a pressure of a refrigerant on the upstream side; a first expansion valve; and a controller. The controller exerts, in an oil recovery operation, an oil recovery first control on the first expansion valve to attain a first opening degree (an opening degree of increasing an opening degree of the usage-side expansion valve in relation to a reduction in the flow rate or the pressure of the refrigerant passing through the first expansion valve), to reduce the flow rate or the pressure of the refrigerant passing through the first expansion valve. The controller exerts an oil recovery second control following the oil recovery first control on the first expansion valve to attain a second opening degree (an opening degree that allows a liquid refrigerant to flow into a usage-side heat exchanger before the opening degree of the usage-side expansion valve is reduced in relation to an increase in the flow rate or the pressure of the refrigerant passing through the first expansion valve), to increase the flow rate or the pressure of the refrigerant passing through the first expansion valve.

TECHNICAL FIELD

The present invention relates to a refrigeration apparatus.

BACKGROUND ART

Conventionally, a refrigeration apparatus including a refrigerantcircuit performing a refrigeration cycle is known. The refrigerantcircuit includes: a heat source unit including a compressor and aheat-source-side heat exchanger; and a service unit including ausage-side heat exchanger and a mechanical expansion valve. Some of suchrefrigeration apparatuses, for example, as a refrigeration apparatusdisclosed in Patent Literature 1 (JP 2009-257759 A), perform at apredetermined timing an oil recovery operation of opening and closing anon-off valve disposed upstream to a mechanical expansion valve in theservice unit to send a liquid refrigerant to the usage-side heatexchanger and to recover a refrigerating machine oil built up in theusage-side heat exchanger.

SUMMARY OF THE INVENTION Technical Problem

In the case where a controller for controlling actuators is disposedoutside the service unit, the refrigeration apparatus which performs theoil recovery operation in the manner disclosed in Patent Literature 1necessitates an electric wire for electrically connecting between theon-off valve in the service unit and the controller in installation ormaintenance. For the troubles and costs in works and maintenancerelating to the electric wire, such refrigeration apparatus is poor inworkability, maintainability, and economy.

An object of the present invention is to provide a refrigerationapparatus which is excellent in workability, maintainability, andeconomy.

Solution to Problem

A refrigeration apparatus according to a first aspect of the presentinvention is a refrigeration apparatus configured to carry out arefrigeration cycle through a refrigerant circuit including a heatsource unit and a service unit. The refrigeration apparatus includes amechanical expansion valve, an electric valve, and a controller. Theheat source unit includes a compressor and a heat-source-side heatexchanger. The compressor is configured to compress a refrigerant. Theheat-source-side heat exchanger functions as a condenser for arefrigerant. The service unit includes a usage-side heat exchanger. Theusage-side heat exchanger functions as an evaporator for a refrigerant.The mechanical expansion valve is disposed on a refrigerant flowupstream side relative to the usage-side heat exchanger. The mechanicalexpansion valve is configured to decompress a refrigerant passingthrough the mechanical expansion valve in accordance with an openingdegree of the mechanical expansion valve. The electric valve is disposedon the refrigerant flow upstream side relative to the mechanicalexpansion valve. The electric valve is configured to adjust a flow rateor a pressure of a refrigerant passing through the electric valve inaccordance with an opening degree of the electric valve. The controlleris configured to control the operation of actuators. The actuatorsinclude the electric valve. The mechanical expansion valve has itsopening degree changed in response to an increase and a reduction in aflow rate or a pressure of a refrigerant flowing on an upstream siderelative to the mechanical expansion valve. The controller executes anoil recovery operation at a predetermined timing. The oil recoveryoperation includes a first control and a second control. The firstcontrol and the second control are control for recovering arefrigerating machine oil built up in the service unit to thecompressor. In the first control, the controller sets the opening degreeof the electric valve to a predetermined first opening degree to reducethe flow rate or the pressure of the refrigerant passing through theelectric valve. The first opening degree is an opening degree thatincreases the opening degree of the mechanical expansion valve inrelation to a reduction in the flow rate or the pressure of therefrigerant passing through the electric valve. In the second control,after the first control, the controller sets the opening degree of theelectric valve to a second opening degree to increase the flow rate orthe pressure of the refrigerant passing through the electric valve. Thesecond opening degree is an opening degree that allows, before theopening degree of the mechanical expansion valve is reduced in relationto an increase in the flow rate or the pressure of the refrigerantpassing through the electric valve, a liquid refrigerant to flow intothe usage-side heat exchanger.

In the refrigeration apparatus according to the first aspect of thepresent invention, in the oil recovery operation, the controller setsthe opening degree of the electric valve to the first opening degree toreduce the flow rate or the pressure of the refrigerant passing throughthe electric valve, and thereafter sets the opening degree of theelectric valve to the second opening degree to increase the flow rate orthe pressure of the refrigerant passing through the electric valve.Thus, in the oil recovery operation, under the first control, inrelation to a reduction in the flow rate or the pressure of therefrigerant passing through the electric valve, the opening degree ofthe mechanical expansion valve is increased. Thereafter, under thesecond control, before the opening degree of the mechanical expansionvalve is reduced in relation to an increase in the flow rate or thepressure of the refrigerant passing through the electric valve, a liquidrefrigerant is allowed to flow into the usage-side heat exchanger. As aresult, the liquid refrigerant flowing into the usage-side heatexchanger is compatibilized with a refrigerating machine oil built up inthe usage-side heat exchanger and is delivered toward the heat sourceunit side. Thus, the refrigerating machine oil is recovered to thecompressor.

That is, it is possible to carry out the oil recovery operation ofrecovering a refrigerating machine oil in the service unit to thecompressor without the necessity of disposing an on-off valve for theoil recovery operation in the service unit (or in a refrigerant flowpath downstream to the heat source unit and upstream to the mechanicalexpansion valve, the same holds true for the following). In other words,in performing the oil recovery operation through the refrigerant circuitincluding the mechanical expansion valve upstream to the usage-side heatexchanger, an on-off valve disposed upstream to the mechanical expansionvalve can be dispensed with. Hence, the refrigeration apparatus candispense with an electric wire for electrically connecting between thecontroller and the on-off valve in installation or maintenance andaccordingly save any troubles and costs in works and maintenancerelating to the electric wire. Hence, the refrigeration apparatus isexcellent in workability, maintainability, and economy.

Note that, while the “refrigerant” as used herein is not limited, it maybe a HFC refrigerant such as R410A or R32, for example.

The refrigeration apparatus according to a second aspect of the presentinvention is the refrigeration apparatus according to the first aspect,in which the controller executes the first control, and executes thesecond control after a lapse of a predetermined time from execution ofthe first control. As used herein, the predetermined time is a time thatis required for the mechanical expansion valve to have its openingdegree increased in response to a reduction in the flow rate or thepressure of the refrigerant passing through the electric valve by thefirst control.

Thus, after the opening degree of the mechanical expansion valve isincreased in relation to the first control being executed, the openingdegree of the electric valve is increased by the second control, wherebya liquid refrigerant by a flow rate suitable for recovering arefrigerating machine oil flows into the usage-side heat exchanger. As aresult, it is possible to carry out the oil recovery operation withoutthe necessity of disposing an on-off valve for the oil recoveryoperation in the service unit. Thus, any electric wire for electricallyconnecting between the controller and the on-off valve in installationor maintenance can be dispensed with, and accordingly, the refrigerationapparatus can save any troubles and costs in works and maintenancerelating to the electric wire.

The refrigeration apparatus according to a third aspect of the presentinvention is the refrigeration apparatus according to the first orsecond aspect, in which the mechanical expansion valve includes a feelerbulb. The feeler bulb is disposed on a refrigerant flow downstream siderelative to the usage-side heat exchanger. The mechanical expansionvalve has its opening degree changed in response to a temperaturedetected by the feeler bulb.

Thus, using the characteristic of the mechanical expansion valveincluding the feeler bulb, a liquid refrigerant is sent to theusage-side heat exchanger to recover a refrigerating machine oil. Thatis, the opening degree of the mechanical expansion valve is notimmediately changed in response to a change in the flow rate of arefrigerant on the upstream side. Instead, the opening degree is changedby a delay corresponding to a response time in response to a change inthe flow rate of the refrigerant on the upstream side (that is, a changein the opening degree of the electric valve). In other words, themechanical expansion valve is characterized by its low-speedresponsivity. By virtue of this characteristic, when the second controlis executed following the first control, the opening degree of themechanical expansion valve is not immediately reduced. Hence, after theelectric valve is set to the second opening degree under the secondcontrol and until the mechanical expansion valve has its opening degreereduced in response thereto, a liquid refrigerant is allowed to flow inby a flow rate suitable for recovering a refrigerating machine oil tothe usage-side heat exchanger.

The refrigeration apparatus according to a fourth aspect of the presentinvention is the refrigeration apparatus according to any one of thefirst to third aspects, in which the electric valve is disposed in theheat source unit. This eliminates the necessity of providing an electricwire for connecting between the heat source unit and the service unitwhich are generally disposed spaced apart from each other. Thisparticularly minimizes works and costs relating to installation ormaintenance.

The refrigeration apparatus according to a fifth aspect of the presentinvention is the refrigeration apparatus according to any one of thefirst to fourth aspects, in which the controller is disposed at the heatsource unit and not electrically connected to any element disposed atthe service unit. This eliminates the necessity of providing an electricwire for connecting between the heat source unit and the service unitwhich are generally disposed spaced apart from each other. Thisparticularly minimizes works and costs relating to installation ormaintenance.

The refrigeration apparatus according to a sixth aspect of the presentinvention is the refrigeration apparatus according to any one of thefirst to fifth aspects. The refrigerant circuit includes a plurality ofthe service units. Thus, even in the case where a plurality of serviceunits are installed (that is, in the case where electric wires arerequired for connecting between the heat source unit and the serviceunits, which involves particularly complicated installation works ormaintenance works), the refrigeration apparatus can dispense with anyelectric wires which are required by an on-off valve for the oilrecovery operation installed in each of the service units. Thisparticularly minimizes works and costs relating to installation ormaintenance.

Advantageous Effects of Invention

Without the necessity of disposing an on-off valve for an oil recoveryoperation in the service unit, the refrigeration apparatus according tothe first aspect of the present invention carries out the oil recoveryoperation of recovering a refrigerating machine oil in the service unitto the compressor. In other words, the mechanical expansion valveperforming an oil recovery operation in the refrigerant circuit disposedupstream to the usage-side heat exchanger does not require an on-offvalve disposed upstream to the mechanical expansion valve. Hence, therefrigeration apparatus can dispense with an electric wire electricallyconnecting between the controller and an on-off valve in installation ormaintenance and, accordingly, the refrigeration apparatus can save anytroubles and costs in works and maintenance relating to the electricwire. Thus, the refrigeration apparatus is excellent in workability,maintainability, and economy.

The refrigeration apparatus according to the second aspect of thepresent invention can dispense with an electric wire for electricallyconnecting between the controller and an on-off valve in installation ormaintenance and, accordingly, the refrigeration apparatus can save anytroubles and costs in works and maintenance relating to the electricwire.

In the refrigeration apparatus according to the third aspect of thepresent invention, using the characteristic of the mechanical expansionvalve including the feeler bulb, a liquid refrigerant is sent to theusage-side heat exchanger to recover the refrigerating machine oil.

The refrigeration apparatus according to the fourth or fifth aspect ofthe present invention can dispense with an electric wire for connectingbetween the heat source unit and the service unit which are generallydisposed spaced apart from each other. This particularly minimizes worksand costs relating to installation or maintenance.

The refrigeration apparatus according to the sixth aspect of the presentinvention can dispense with an electric wire which is required for anon-off valve for an oil recovery operation in each of the service units,even in the case where a plurality of service units are provided. Thisparticularly minimizes works and costs relating to installation ormaintenance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a refrigeration apparatusaccording to one embodiment of the present invention.

FIG. 2 is a block diagram schematically showing a schematicconfiguration of a controller and units connected to the controller.

FIG. 3 is a flowchart showing an exemplary flow of processes at thecontroller.

DESCRIPTION OF EMBODIMENTS

In the following, with reference to the drawings, a description will begiven of a refrigeration apparatus 100 according to an embodiment of thepresent invention. Note that, the following embodiment is merely aspecific example of the present invention and does not limit thetechnical scope of the present invention. Any changes can be made asappropriate within a range not deviating from the spirit of theinvention.

(1) Refrigeration Apparatus 100

FIG. 1 is a schematic configuration diagram of the refrigerationapparatus 100 according to an embodiment of the present invention. Therefrigeration apparatus 100 is configured to cool, by a vaporcompression refrigeration cycle, the inside of a low-temperaturewarehouse, the inside of a showcase at a shop, the usage-side space (thetarget space) formed in a transfer container or the like. Therefrigeration apparatus 100 mainly includes a heat source unit 10, aplurality of (two in the present embodiment) service units 30 (30 a, 30b), and a controller 50 controlling the operation of the refrigerationapparatus 100.

In the refrigeration apparatus 100, a refrigerant circuit RC is formedby one heat source unit 10 and the service units 30 being connected toeach other via a gas-side connection pipe G1 and a liquid-sideconnection pipe L1. The refrigeration apparatus 100 carries out arefrigeration cycle of subjecting a refrigerant enclosed in therefrigerant circuit RC to compression, cooling or condensation,decompression, and heating or evaporation, and thereafter againcompression. The refrigerant enclosed in the refrigerant circuit RC is,for example, an HFC refrigerant such as R32 or R410A.

(1-1) Heat Source Unit 10 (1-1-1) Circuit Elements Disposed at HeatSource Unit 10

The heat source unit 10 is connected to the service units 30 via thegas-side connection pipe G1 and the liquid-side connection pipe L1 toform part of the refrigerant circuit RC. The heat source unit 10 mainlyincludes, as circuit elements forming the refrigerant circuit RC, aplurality of (in the present embodiment, three) compressors 11 (a firstcompressor 11 a, a second compressor 11 b, a third compressor 11 c), aheat-source-side heat exchanger 12, a receiver 13, a subcooling heatexchanger 14, a first expansion valve 15, a second expansion valve 16,injection valves 17 (a first injection valve 17 a, a second injectionvalve 17 b, a third injection valve 17 c) as many as the compressors 11(in the present embodiment, three), a gas-side shutoff valve SV1, and aliquid-side shutoff valve SV2.

The compressors 11 take in and compress a low-pressure refrigerant in arefrigeration cycle, and discharge the compressed refrigerant as ahigh-pressure refrigerant. The compressors 11 are each, for example, ascroll-type compressor, and each have a closed configuration in which acompression element (not shown) is rotated as being linked to acompressor motor (not shown) in a casing. In the present embodiment, thefirst compressor 11 a, the second compressor 11 b, and the thirdcompressor 11 c are each a “variable-capacity compressor” whoseoperating capacity is variable, that is, which has, in operation, thenumber of revolutions of the compressor motor controlled as appropriateby an inverter. Alternatively, the second compressor 11 b and the thirdcompressor 11 c are each a “constant-capacity compressor” whoseoperating capacity is constant, that is, the number of revolutions ofthe compressor motor in operation is constant. The first compressor 11a, the second compressor 11 b, and the third compressor 11 c aredisposed in parallel to one another.

Note that, while the refrigerating machine oil (the lubricant of thecompressors 11) is not specified, it may be, for example, an ester oilhaving an ester bond, a carbonate oil, a polyalkylene glycol oil (PAG)having an ether bond, or a polyvinyl ether oil.

The heat-source-side heat exchanger 12 is a heat exchanger thatfunctions as a radiator or a condenser for the high-pressure refrigerantin the refrigeration cycle. The heat-source-side heat exchanger 12includes a heat transfer tube (not shown) through which a refrigerantflows, and is configured to allow the refrigerant in the heat transfertube and an air flow generated by the heat-source-side fan 19 (describedlater) to exchange heat with each other.

The receiver 13 is a container that temporarily stores the refrigerantflowed out from the heat-source-side heat exchanger 12. In the receiver13, a refrigerant reservoir space is formed. The refrigerant reservoirspace has the capacity corresponding to the amount of the refrigerantenclosed in the refrigerant circuit RC.

The subcooling heat exchanger 14 is, for example, a double pipe heatexchanger. The subcooling heat exchanger 14 is provided with tworefrigerant flow paths (a first flow path 141 and a second flow path142). The first flow path 141 is a path through which a refrigerantflowed out from the receiver 13 passes. The second flow path 142 is aflow path through which an intermediate-pressure refrigerant havingpassed through the first flow path 141 and thereafter decompressed bythe second expansion valve 16 passes. The subcooling heat exchanger 14is configured to allow a refrigerant in the first flow path 141 and arefrigerant in the second flow path 142 to exchange heat with eachother.

The first expansion valve 15 (corresponding to the “electric valve” inthe claims) is an electric valve whose opening degree is controllable.In accordance with the opening degree of the first expansion valve 15,the refrigerant passing therethrough is decompressed, or the flow rateof the refrigerant passing therethrough is increased or reduced. Thefirst expansion valve 15 decompresses a high-pressure liquid refrigeranthaving passed through the first flow path 141 of the subcooling heatexchanger 14 to provide a low-pressure gas-liquid two-phase refrigerant.The first expansion valve 15 is disposed on the upstream side in theliquid-side connection pipe L1 extending to the service units 30, andadjusts the pressure and the flow rate of the refrigerant sent to theservice units 30 via the liquid-side connection pipe L1.

The second expansion valve 16 is an electric valve whose opening degreeis controllable. In accordance with the opening degree of the secondexpansion valve 16, the refrigerant passing therethrough isdecompressed, or the flow rate of the refrigerant passing therethroughis increased or reduced. The second expansion valve 16 decompresses ahigh-pressure liquid refrigerant having passed through the first flowpath 141 of the subcooling heat exchanger 14 to provide anintermediate-pressure gas-liquid two-phase refrigerant or liquidrefrigerant (an intermediate-pressure refrigerant). The second expansionvalve 16 is disposed on the refrigerant flow upstream side in therefrigerant pipe (a twelfth pipe P12 which will be described later)upstream to the injection valve 17.

The injection valves 17 are electric expansion valves whose openingdegree is controllable. In accordance with the opening degree of theinjection valves 17, the refrigerant passing therethrough isdecompressed, or the flow rate of the refrigerant passing therethroughis increased or reduced. The injection valves 17 have their respectiveone ends connected to corresponding injection pipes (fourth pipes P4which will be described later) of the compressors 11, and adjust theflow rate of the intermediate-pressure refrigerant passing through.Here, the first injection valve 17 a corresponds to the first compressor11 a and a fourth pipe P4 a (described later). The second injectionvalve 17 b corresponds to the second compressor 11 b and a fourth pipeP4 b (described later). The third injection valve 17 c corresponds tothe third compressor 11 c and a fourth pipe P4 c (described later).

The gas-side shutoff valve SV1 is a manual valve connected to one end ofthe gas-side connection pipe G1. The liquid-side shutoff valve SV2 is amanual valve connected to one end of the liquid-side connection pipe L1.

(1-1-2) Refrigerant Pipe Disposed at Heat Source Unit 10

The heat source unit 10 includes a plurality of refrigerant pipesconnecting between the circuit elements. Specifically, the heat sourceunit 10 includes a first pipe P1, second pipes P2 (P2 a, P2 b, P2 c),third pipes P3 (P3 a, P3 b, P3 c), and fourth pipes P4 (P4 a, P4 b, P4c) as many as (three) the compressors 11, and a fifth pipe P5 to atwelfth pipe P12.

The first pipe P1 connects between one end of the gas-side shutoff valveSV1 and individual one ends of the second pipes P2 (intake pipes).

Each of the second pipes P2 corresponds to any of the compressors 11 andis connected to the intake port of the corresponding compressor 11. Eachsecond pipe P2 functions as an intake pipe through which a low-pressurerefrigerant flowing into the corresponding compressor 11 flows. Thesecond pipe P2 a corresponds to the first compressor 11 a. The secondpipe P2 b corresponds to the second compressor 11 b. The second pipe P2c corresponds to the third compressor 11 c.

Each of the third pipes P3 corresponds to any of the compressors 11 andis connected to a discharge port of the corresponding compressor 11.Each third pipe P3 functions as a discharge pipe through which ahigh-pressure refrigerant discharged from the corresponding compressor11 flows. The third pipe P3 a corresponds to the first compressor 11 a.The third pipe P3 b corresponds to the second compressor 11 b. The thirdpipe P3 c corresponds to the third compressor 11 c.

Each of the fourth pipes P4 corresponds to any of the compressors 11 andis connected to an injection port of the corresponding compressor 11.Each fourth pipe P4 functions as an injection pipe that allows anintermediate-pressure refrigerant to flow into a compression chamber ofthe corresponding compressor 11. The fourth pipe P4 a corresponds to thefirst compressor 11 a. The fourth pipe P4 b corresponds to the secondcompressor 11 b. The fourth pipe P4 c corresponds to the thirdcompressor 11 c.

The fifth pipe P5 connects between one ends of the third pipes P3 andthe gas side of the heat-source-side heat exchanger 12.

The sixth pipe P6 connects between the liquid side of theheat-source-side heat exchanger 12 and a refrigerant inflow port of thereceiver 13.

The seventh pipe P7 connects between a refrigerant outflow port of thereceiver 13 and one end of the first flow path 141 of the subcoolingheat exchanger 14.

The eighth pipe P8 connects between other end of the first flow path 141of the subcooling heat exchanger 14 and one end of the first expansionvalve 15.

The ninth pipe P9 connects between other end of the first expansionvalve 15 and one end of the liquid-side shutoff valve SV2.

The tenth pipe P10 extends from a point between the opposite ends of theeighth pipe P8 and is connected to one end of the second expansion valve16.

The eleventh pipe P11 connects between other end of the second expansionvalve 16 and one end of the second flow path 142 of the subcooling heatexchanger 14.

The twelfth pipe P12 connects between other end of the second flow path142 of the subcooling heat exchanger 14 and individual other ends of theinjection valves 17. In more detail, the twelfth pipe P12 has its oneend connected to the second flow path 142, and its other end branched inthree ways and individually connected to the injection valves 17.

Note that, in the refrigerant circuit RC, the tenth pipe P10, the secondexpansion valve 16, the eleventh pipe P11, the second flow path 142 ofthe subcooling heat exchanger 14, the twelfth pipe P12, the injectionvalves 17, and the fourth pipes P4 form an injection line J1. Theinjection line J1 is a refrigerant flow path for allowing part of therefrigerant flowing through the eighth pipe P8 to branch and flow (beinjected) into the compressors 11.

(1-1-3) Other Elements Disposed at Heat Source Unit 10

The heat source unit 10 includes a heat-source-side fan 19 thatgenerates an air flow that flows from the outside of the heat sourceunit 10 into the heat source unit 10, passes through theheat-source-side heat exchanger 12, and then flows to the outside fromthe heat source unit 10. The heat-source-side fan 19 is a fan forsupplying the heat-source-side heat exchanger 12 with air as the coolingsource for a refrigerant flowing through the heat-source-side heatexchanger 12. The heat-source-side fan 19 is, for example, a propellerfan or a sirocco fan, and rotates as being linked with aheat-source-side fan motor (not shown).

The heat source unit 10 further includes various types of sensors suchas a low-pressure side pressure sensor 21, a high-pressure side pressuresensor 22, an intermediate pressure sensor 23, and a plurality ofdischarge temperature sensors 25 (a first discharge temperature sensor25 a, a second discharge temperature sensor 25 b, a third dischargetemperature sensor 25 c).

The low-pressure side pressure sensor 21 is disposed at the first pipeP1 (a low-pressure-side refrigerant pipe) on the refrigerant flowupstream side relative to the intake pipes (P2 a, P2 b, P2 c) of thecompressors 11. The low-pressure side pressure sensor 21 detects alow-pressure-side pressure LP which is the pressure of the refrigerantpassing through the first pipe P1 (that is, the low-pressure refrigeranton the intake side of the compressors 11).

The high-pressure side pressure sensor 22 is disposed at the fifth pipeP5 on the refrigerant flow downstream side relative to the dischargepipes (P3 a, P3 b, P3 c) of the compressors 11. The high-pressure sidepressure sensor 22 detects a high-pressure-side pressure HP which is thepressure of the refrigerant passing through the fifth pipe P5 (that is,the high-pressure refrigerant on the discharge side of the compressors11).

The intermediate pressure sensor 23 is disposed at the twelfth pipe P12(an upstream side common pipe) on the refrigerant flow upstream siderelative to the injection pipes (P4 a, P4 b, P4 c) of the compressors11. The intermediate pressure sensor 23 detects an intermediate pressureMP which is the pressure of the refrigerant passing through the twelfthpipe P12 (that is, the intermediate-pressure refrigerant flowing intothe injection valves 17).

The discharge temperature sensors 25 are disposed at the discharge pipes(P3 a, P3 b, or P3 c) of corresponding ones of the compressors 11 anddetect the temperature of a high-pressure refrigerant discharged fromthe corresponding ones of the compressors 11 (a discharged refrigeranttemperature HT). The first discharge temperature sensor 25 a correspondsto the first compressor 11 a. The second discharge temperature sensor 25b corresponds to the second compressor 11 b. The third dischargetemperature sensor 25 c corresponds to the third compressor 11 c.

(1-2) Service Units 30

The service units 30 are connected to the heat source unit 10 via thegas-side connection pipe G1 and the liquid-side connection pipe L1, andform part of the refrigerant circuit RC. In the present embodiment, toone heat source unit 10, two service units 30 (30 a, 30 b) areconnected. The service units 30 are connected in parallel to each other.

The service units 30 each mainly include, as circuit elements formingthe refrigerant circuit RC, a usage-side expansion valve 31 and ausage-side heat exchanger 32.

(1-2-1) Usage-Side Expansion Valve 31

The usage-side expansion valve 31 is a throttling mechanism thatfunctions as means for decompressing (means for expanding) a refrigerantsent from the heat source unit 10 (corresponding to the “mechanicalexpansion valve” in the claims). In accordance with its opening degree,the usage-side expansion valve 31 decompresses the refrigerant thatpasses therethrough. The usage-side expansion valve 31 is a thermostaticexpansion valve that includes a valve body 311 formed of a valveelement, a diaphragm and the like, a feeler bulb 312 having enclosedtherein a refrigerant similar to that flowing through the refrigerantcircuit RC, and a capillary tube 313 establishing communication betweenthe valve body 311 and the feeler bulb 312. The usage-side expansionvalve 31 may be a known general valve as the one disclosed in JPH10-184982 A, for example. Details of the usage-side expansion valve 31will be given later.

(1-2-2) Usage-Side Heat Exchanger 32

The usage-side heat exchanger 32 is a heat exchanger that functions asan evaporator for a low-pressure refrigerant in the refrigeration cycle,to cool the air in the usage-side space. The usage-side heat exchanger32 includes a heat transfer tube (not shown) through which a refrigerantflows, and is configured to allow the refrigerant in the heat transfertube and an air flow generated by a usage-side fan 35 (described later)to exchange heat with each other.

(1-2-3) Refrigerant Pipes Disposed at Service Units 30

The service units 30 each include a plurality of refrigerant pipesconnecting between the circuit elements. Specifically, each service unit30 includes a thirteenth pipe P13, a fourteenth pipe P14, and afifteenth pipe P15.

The thirteenth pipe P13 connects between other end of the liquid-sideconnection pipe L1 and one end of the usage-side expansion valve 31.Note that, other end of the liquid-side connection pipe L1 branches inaccordance with the number of the service units 30, to connect torespective thirteenth pipes P13 of the service units 30.

The fourteenth pipe P14 connects between other end of the usage-sideexpansion valve 31 and a liquid-side gate of the usage-side heatexchanger 32.

The fifteenth pipe P15 connects between a gas-side gate of theusage-side heat exchanger 32 and other end of the gas-side connectionpipe G1. Note that, other end of the gas-side connection pipe G1branches in accordance with the number of the service units 30, toconnect to respective fifteenth pipes P15 of the service units 30.

(1-2-4) Other Elements Disposed at Service Units 30

The service units 30 each include a usage-side fan 35 that generates anair flow passing through the usage-side heat exchanger 32. Theusage-side fan 35 is a fan for supplying the usage-side heat exchanger32 with air as the heating source for a refrigerant flowing through theusage-side heat exchanger 32. The usage-side fan 35 is, for example, acentrifugal fan or a sirocco fan, and rotates as being linked to ausage-side fan motor (not shown). The usage-side fan 35 is electricallyconnected to an independent power source (a commercial power source, astorage battery or the like), and operates by being supplied with power.

(1-3) Controller 50

The controller 50 is a control unit configured to control the operationstate of the refrigeration apparatus 100 by controlling the operation ofthe actuators included in the refrigeration apparatus 100. Thecontroller 50 includes a microcomputer which includes a CPU, a memoryand the like. In the present embodiment, the controller 50 is disposedat the heat source unit 10. The controller 50 is electrically connectedto the actuators included in the refrigeration apparatus 100, toexchange signals via a predetermined interface. The controller 50 isfurther electrically connected to various types of sensors included inthe refrigeration apparatus 100, to receive signals corresponding todetection results as appropriate. Details of the controller 50 will begiven later.

(2) Flow of Refrigerant in Refrigerant Circuit RC in Cooling Operation

In the following, a description will be given of the flow of therefrigerant in the refrigerant circuit RC in operation. In therefrigeration apparatus 100, in operation, in accordance with therequired cooling load in the service units 30, the variable-capacitycompressor out of the compressors 11 has its capacity controlled, andthe constant-capacity compressor performs a rated operation.Specifically, the number of the compressors 11 in operation and theoperating capacity of the variable-capacity compressor are controlled soas to satisfy respective target values of the low-pressure-side pressureLP, the high-pressure-side pressure HP, and/or the intermediate pressureMP, which target values are set in accordance with the required coolingload in the service units 30. Thus, a cooling operation (a refrigerationcycle operation) is carried out in which the refrigerant enclosed in therefrigerant circuit RC mainly circulates, in sequence, any of thecompressors 11 in operation, the heat-source-side heat exchanger 12, thereceiver 13, the subcooling heat exchanger 14 (the first flow path 141),the first expansion valve 15, the usage-side expansion valve 31, and theusage-side heat exchanger 32.

In the cooling operation, a refrigerant is taken into the compressor 11in operating via the intake pipe (P2 a, P2 b, or P2 c) to be compressed,and then discharged as a high-pressure refrigerant. Here, the lowpressure in the refrigeration cycle is the low-pressure-side pressure LPdetected by the low-pressure side pressure sensor 21. The high pressureis the high-pressure-side pressure HP detected by the high-pressure sidepressure sensor 22. The intermediate pressure is the intermediatepressure MP detected by the intermediate pressure sensor 23.

Each of the gas refrigerant discharged from the compressors 11 flowsthrough corresponding ones of discharge pipes (P3 a, P3 b, P3 c), tomerge with each other at the fifth pipe P5 and flows into the gas-sidegate of the heat-source-side heat exchanger 12. Note that, in each ofthe operating compressors 11 in operation, an intermediate-pressurerefrigerant is injected into the compression chamber via the injectionpipe (the fourth pipe P4), so as to control the temperature of thedischarged high-pressure refrigerant to attain the target value.

The gas refrigerant flowing into the gas-side gate of theheat-source-side heat exchanger 12 exchanges, in the heat-source-sideheat exchanger 12, heat with air supplied by the heat-source-side fan19. Thus, the gas refrigerant radiates heat, condenses, becomes a liquidrefrigerant or a gas-liquid two-phase refrigerant of a high pressure,and then flows out from the liquid-side gate of the heat-source-sideheat exchanger 12. The refrigerant flowed out from the liquid-side gateof the heat-source-side heat exchanger 12 flows into the refrigerantinflow port of the receiver 13 via the sixth pipe P6. The refrigerantflowed into the receiver 13 is temporarily stored at the receiver 13 asa saturated liquid refrigerant, and then flows out from the refrigerantoutflow port of the receiver 13.

The liquid refrigerant flowed out from an outflow port of the receiver13 passes through the seventh pipe P7 to flow into the first flow path141 of the subcooling heat exchanger 14. The liquid refrigerant flowinginto the first flow path 141 of the subcooling heat exchanger 14exchanges heat with a refrigerant flowing through the second flow path142 in the subcooling heat exchanger 14 to be further cooled. Thus, theliquid refrigerant becomes a subcooled liquid refrigerant and isdischarged from the subcooling heat exchanger 14.

The subcooled liquid refrigerant flowed out from the subcooling heatexchanger 14 flows through the eighth pipe P8. The refrigerant flowingthrough the eighth pipe P8 branches into two flows. In the two flows ofthe refrigerant branched from the eighth pipe P8, one flow flows intothe first expansion valve 15. The refrigerant flowing into the firstexpansion valve 15 is decompressed in accordance with the opening degreeof the first expansion valve 15, to become a low-pressure gas-liquidtwo-phase refrigerant. The gas-liquid two-phase refrigerant havingpassed through the first expansion valve 15 passes through the ninthpipe P9 and the liquid-side shutoff valve SV2, and is discharged fromthe heat source unit 10.

On the other hand, in the flow of the refrigerant branched from theeighth pipe P8, other flow flows into the injection line J1. Therefrigerant flowing into the injection line J1 passes through the tenthpipe P10 to flow into the second expansion valve 16. The refrigerantflowing into the second expansion valve 16 is decompressed in accordancewith the opening degree of the second expansion valve 16, to become aliquid refrigerant or a gas-liquid two-phase refrigerant of anintermediate pressure. The refrigerant having passed through the secondexpansion valve 16 flows through the eleventh pipe P11 to flow into thesecond flow path 142 of the subcooling heat exchanger 14. Note that, theflow rate and the pressure of the refrigerant flowing through theinjection line J1 fluctuate mainly on the basis of the opening degree ofthe second expansion valve 16, the opening degree of the injectionvalves 17, the frequency of the compressors 11 in operation, and thelike.

The liquid refrigerant flowing into the second flow path 142 of thesubcooling heat exchanger 14 exchanges heat with the refrigerant flowingthrough the first flow path 141 in the subcooling heat exchanger 14thereby heated, to become a gas-liquid two-phase refrigerant or a gasrefrigerant of an intermediate pressure, and flows out from thesubcooling heat exchanger 14. The gas-liquid two-phase refrigerant orthe gas refrigerant of an intermediate pressure flowed out from thesubcooling heat exchanger 14 flows through the twelfth pipe P12. Notethat, the flow rate and the pressure of the refrigerant flowing throughthe second flow path 142 of the subcooling heat exchanger 14 and thetwelfth pipe P12 increase or reduce in accordance with the openingdegree of the second expansion valve 16.

The refrigerant flowing through the twelfth pipe P12 branches into threeflows, which flows respectively flow into the injection valves 17. Therefrigerant flowed into the injection valves 17 is decompressed or hasits flow rate adjusted in accordance with the opening degree of theinjection valves 17, and flows through the injection pipes (the fourthpipes P4) to be injected into the compression chamber of correspondingones of the compressors 11. Note that, this injection is performed forthe purpose of controlling the temperature of the refrigerant dischargedfrom the compressors 11 to attain the target value.

The low-pressure two-phase refrigerant flowed out from the heat sourceunit 10 passes through the liquid-side connection pipe L1 to flow intothe operating ones of the service units 30. The refrigerant flowed intoeach service unit 30 passes through the thirteenth pipe P13 to flow intothe valve body 311 of the usage-side expansion valve 31, and isdecompressed or has its flow rate adjusted in accordance with theopening degree of the valve body 311. Note that, the opening degree ofthe valve body 311 increases or reduces in accordance with the degree ofsuperheating of a refrigerant in the fifteenth pipe P15 where the feelerbulb 312 is disposed. The refrigerant having passed through the valvebody 311 of the usage-side expansion valve 31 flows through thefourteenth pipe P14 to flow into the liquid-side gate of the usage-sideheat exchanger 32.

The refrigerant flowed into the liquid-side gate of the usage-side heatexchanger 32 exchanges heat with air supplied by the usage-side fan 35in the usage-side heat exchanger 32 thereby evaporated, to become alow-pressure gas refrigerant and flows out from the gas-side gate of theusage-side heat exchanger 32. The gas refrigerant flowed out from thegas-side gate of the usage-side heat exchanger 32 flows through thefifteenth pipe P15 and flows out from the service unit 30.

The refrigerant flowed out from each service unit 30 flows through thegas-side connection pipe G1 and the gas-side shutoff valve SV1 to flowinto the heat source unit 10. The refrigerant flowing into the heatsource unit 10 flows through the first pipe P1 and the second pipe P2,and again taken into the operating ones of the compressors 11.

(3) Details of Usage-Side Expansion Valve 31

In the usage-side expansion valve 31, the valve body 311 is disposed onthe liquid-side gate side (the refrigerant flow upstream side) relativeto the usage-side heat exchanger 32, and the feeler bulb 312 is disposedon the gas-side gate side (the refrigerant flow downstream side)relative to the usage-side heat exchanger 32. In other words, theusage-side expansion valve 31 is disposed on the refrigerant flowdownstream side relative to the first expansion valve 15.

The state of the refrigerant in the feeler bulb 312 changes inaccordance with the detected temperature at the feeler bulb 312 (in thepresent embodiment, the temperature of the refrigerant flowing out fromthe gas-side gate of the usage-side heat exchanger 32). The valve body311 and the feeler bulb 312 communicate with each other via thecapillary tube 313. A diaphragm in the valve body 311 actuates inaccordance with the change in the state of the refrigerant in the feelerbulb 312. This determines the opening degree of the valve element. Notethat, the valve body 311 includes therein a spring that biases the valveelement. The biasing force of the spring is adjustable by an adjustscrew.

When the flow rate of the refrigerant flowing into the service unit 30reduces, the flow rate of the refrigerant passing through the valve body311 reduces. In relation thereto, the degree of superheating at theusage-side heat exchanger 32 increases. In response thereto, the openingdegree of the valve body 311 is increased. Here, the flow rate of therefrigerant flowing into the service unit 30 reduces in response to areduction in the flow rate of the refrigerant passing through the firstexpansion valve 15. That is, by the opening degree of the firstexpansion valve 15 being reduced, the flow rate of the refrigerantflowing into the service unit 30 reduces. In relation thereto, thedegree of superheating at the usage-side heat exchanger 32 increases andthe opening degree of the valve body 311 is increased.

By the opening degree of the first expansion valve 15 being reduced, thepressure of the refrigerant passing through the first expansion valve 15reduces and the pressure of the refrigerant flowing into the serviceunit 30 reduces. That is, when the opening degree of the first expansionvalve 15 is reduced, the flow rate and the pressure of the refrigerantpassing through the first expansion valve 15 reduce and the degree ofsuperheating at the usage-side heat exchanger 32 increases, whereby theopening degree of the valve body 311 is increased. In other words, theusage-side expansion valve 31 is disposed so that its opening degree isincreased in response to a reduction in the flow rate or the pressure ofthe refrigerant flowing through the first expansion valve 15.

On the other hand, when the flow rate of the refrigerant flowing intothe service unit 30 increases, the flow rate of the refrigerant passingthrough the valve body 311 increases. In relation thereto, the degree ofsuperheating at the usage-side heat exchanger 32 reduces. In responsethereto, the opening degree of the valve body 311 is reduced. Here, theflow rate of the refrigerant flowing into the service unit 30 increasesin response to an increase in the flow rate of the refrigerant passingthrough the first expansion valve 15 (that is, an increase in theopening degree of the first expansion valve 15). Furthermore, by theopening degree of the first expansion valve 15 being increased, thepressure of the refrigerant passing through the first expansion valve 15increases, and the pressure of the refrigerant flowing into the serviceunit 30 increases. That is, by the opening degree of the first expansionvalve 15 being increased, the flow rate and the pressure of therefrigerant flowing into the service unit 30 increase. In relationthereto, the degree of superheating at the usage-side heat exchanger 32reduces, whereby the opening degree of the valve body 311 is reduced.

In this manner, the usage-side expansion valve 31 has its opening degreechanged in direct response to an increase or reduction in the degree ofsuperheating of the refrigerant flowing out from the usage-side heatexchanger 32 (that is, an increase or reduction in the flow rate of therefrigerant flowing into the service unit 30). From a broad view, it canbe regarded that the usage-side expansion valve 31 has its openingdegree changed in response to an increase or reduction in the pressureof the refrigerant flowing into the service unit 30. That is, theopening degree of the usage-side expansion valve 31 is changed inresponse to an increase or reduction in the opening degree of the firstexpansion valve 15.

Note that, because of its structure, the opening degree of theusage-side expansion valve 31 is not immediately changed upon a changein the opening degree of the first expansion valve 15. An increase orreduction in the degree of superheating at the usage-side heat exchanger32 takes place in response to a change in the opening degree of thefirst expansion valve 15, and the feeler bulb 312 detects that change inthe degree of superheating. Then, the opening degree of the usage-sideexpansion valve 31 is changed. That is, the opening degree of theusage-side expansion valve 31 is changed with a delay corresponding to apredetermined response time for a change in the opening degree of thefirst expansion valve 15. This response time varies depending on theconfiguration of the usage-side expansion valve 31, the length of therefrigerant pipes, the capacity of the usage-side heat exchanger 32, theairflow volume of the usage-side fan 35, and/or the type of therefrigerant, and the like.

(4) Details of Controller 50

FIG. 2 is a block diagram schematically showing the schematicconfiguration of the controller 50 and units connected to the controller50.

The controller 50 has a plurality of control modes, and controls theoperation of the refrigeration apparatus 100 corresponding to thecurrent control mode. For example, the controller 50 has, as the controlmodes, a normal mode in a normal operation, and an oil recovery controlmode to which the controller 50 transitions from the normal mode when anoil recovery operation start condition (described later) is satisfied.

The controller 50 is electrically connected to actuators included in theheat source unit 10 (specifically, the compressors 11, the firstexpansion valve 15, the second expansion valve 16, the injection valves17, the heat-source-side fan 19 and the like), and various types ofsensors (the low-pressure side pressure sensor 21, the high-pressureside pressure sensor 22, the intermediate pressure sensor 23, thedischarge temperature sensors 25 and the like). The controller 50 isfurther electrically connected to a command input apparatus such as aremote controller, which is not shown. Note that, in the presentembodiment, the controller 50 is not electrically connected to theelements disposed in the service unit 30.

The controller 50 mainly includes a storage unit 51, an input controlunit 52, a mode control unit 53, and an actuator control unit 54. Notethat, these units in the controller 50 are implemented by the elementsforming the controller 50 (a CPU, various types of memory, acommunication module, various types of interfaces, various types ofelectric components and the like) organically functioning.

(4-1) Storage Unit 51

The storage unit 51 is formed of, for example, various types of memorysuch as, for example, ROM, RAM, and/or flash memory, and includes aplurality of storage regions. For example, the storage unit 51 includesa program storage region 511 for storing a control program in whichprocesses at the units of the controller 50 are defined.

The storage unit 51 further includes a detected value storage region 512for storing detected values from various types of sensors, and a commandstorage region 513 for storing any input command.

The storage unit 51 further includes a characteristic informationstorage region 514 for storing the characteristic of the usage-sideexpansion valve 31. The characteristic information storage region 514stores, for example, information (usage-side expansion valvecharacteristic information) on the opening degree characteristic of theusage-side expansion valve 31 (the correlation between the degree ofsuperheating of a refrigerant flowing out from the usage-side heatexchanger 32 or the opening degree of the first expansion valve 15 andthe opening degree of the usage-side expansion valve 31) and theresponse characteristic (for example, the response time of theusage-side expansion valve 31 to a change in the opening degree of thefirst expansion valve 15).

The storage unit 51 is provided with a plurality of flags havingpredetermined number of bits. For example, the storage unit 51 isprovided with a control mode determination flag 515 with which thecurrent control mode of the controller 50 is determined. The controlmode determination flag 515 includes the number of bits corresponding tothe number of the control modes, and sets a bit corresponding to thecurrent control mode. This allows the units to determine the currentcontrol mode.

The storage unit 51 is further provided with an oil recovery operationfirst flag 516 for determining whether or not a start executioncondition on an oil recovery operation (an oil recovery operation startcondition) for recovering the refrigerating machine oil from the serviceunits 30 to the compressors 11 is satisfied (that is, whether or not toexecute the oil recovery operation). The oil recovery operation firstflag 516 is set when the oil recovery operation start condition issatisfied.

The storage unit 51 is further provided with an oil recovery operationsecond flag 517 for determining whether or not an oil recovery firstcontrol (described later) in the oil recovery operation has beencompleted and a start execution condition (a second control startcondition) for an oil recovery second control (described later) issatisfied (that is, whether or not to execute the oil recovery secondcontrol). The oil recovery operation second flag 517 is set when thesecond control start condition is satisfied.

(4-2) Input Control Unit 52

The input control unit 52 is a functional unit that functions as aninterface for accepting signals from any elements connected to thecontroller 50. For example, the input control unit 52 receives a signalcorresponding to a detection result output from any of the various typesof sensors (21-23, 25 and the like), attaches predeterminedidentification data thereto and stores the same individually in thedetected value storage region 512. For example, the input control unit52 receives a signal from a command input apparatus which is not shown,and stores the same individually in the command storage region 513.

(4-3) Mode Control Unit 53

The mode control unit 53 is a functional unit that switches the controlmode. When the oil recovery operation start condition is satisfied inthe normal mode, the mode control unit 53 sets the oil recoveryoperation first flag 516. Thus, the control mode transitions to the oilrecovery control mode, and the oil recovery first control (describedlater) is executed.

The oil recovery operation start condition is a condition satisfied bythe refrigerating machine oil being built up in the service units 30 (inparticular, the usage-side heat exchangers 32). For example, the oilrecovery operation start condition is satisfied by a lapse of apredetermined time (the time indicating that the refrigerating machineoil has built up in the service units 30) in a cooling operation.Furthermore, for example, the oil recovery operation start condition issatisfied by, in a cooling operation, any detected value of varioustypes of sensors (21, 22, 23, or 25) attaining a predetermined referencevalue (a value indicating that the refrigerating machine oil has builtup in the service units 30).

When the mode control unit 53 is in the oil recovery control mode, by apredetermined second control start condition being satisfied, the modecontrol unit 53 sets the oil recovery operation second flag 517. Thisends the oil recovery first control in the oil recovery operation, andstarts the oil recovery second control (described later).

The second control start condition is a condition satisfied by the oilrecovery first control being completed. Specifically, the second controlstart condition is a condition satisfied by the opening degree of theusage-side expansion valve 31 being increased in response to the firstexpansion valve 15 set to a first opening degree under the oil recoveryfirst control which will be described later. In the present embodiment,the oil recovery operation end condition is satisfied by, in the oilrecovery first control of the oil recovery operation, a lapse of apredetermined time (a predetermined first time t1 indicating that theopening degree of the usage-side expansion valve 31 has attained amaximum opening degree). The first time t1 is a time which is necessaryfor the opening degree of the usage-side expansion valve 31 to beincreased, by the oil recovery first control, in response to a reductionin the flow rate or the pressure of a refrigerant passing through thefirst expansion valve 15. The first time t1 is set on the basis of theusage-side expansion valve characteristic information. In the presentembodiment, the first time t1 is set to three minutes.

When the mode control unit 53 is in the oil recovery control mode, themode control unit 53 clears the oil recovery operation first flag 516and the oil recovery operation second flag 517 by a predetermined oilrecovery operation end condition being satisfied. This ends the oilrecovery operation.

The oil recovery operation end condition is a condition satisfied by therecovery of the refrigerating machine oil in the service units 30(particularly the usage-side heat exchangers 32) to the compressors 11being completed. In the present embodiment, the oil recovery operationend condition is satisfied by, in the oil recovery second control whichwill be described later, a lapse of a predetermined time (a second timet2). The second time t2 is a time which is necessary for the increasedopening degree of the usage-side expansion valve 31 to be reduced, bythe oil recovery second control, to cause the liquid refrigerant tobecome less prone to flow into the usage-side heat exchanger 32. Thesecond time t2 is set on the basis of the usage-side expansion valvecharacteristic information. In the present embodiment, the second timet2 is set to three minutes.

The mode control unit 53 switches the control mode to the normal mode,unless the control mode is in the oil recovery control mode.

(4-4) Actuator Control Unit 54

The actuator control unit 54 controls, as circumstances demand inaccordance with the control program, the operation of the actuatorsincluded in the refrigeration apparatus 100 (the heat source unit 10 andthe service units 30). For example, the actuator control unit 54controls, in real time, the number of revolutions of the compressors 11,the number of revolutions of the heat-source-side fan 19 and theusage-side fans 35, the opening degree of the first expansion valve 15,the opening degree of the second expansion valve 16, and the openingdegree of the usage-side expansion valves 31 in accordance with the settemperature, the type of commands, the magnitude of the cooling load,the detected values of the sensors (21, 22, 23, 25) and the like.

The actuator control unit 54 includes a plurality of functional units.For example, the actuator control unit 54 includes a drive signal outputunit 55 and a first expansion valve control unit 56.

(4-4-1) Drive Signal Output Unit 55

The drive signal output unit 55 is a functional unit that outputs apredetermined drive signal (drive voltage) to the actuators (11 a to 11c, 15, 16, 17 a to 17 c, 19 and the like). The drive signal output unit55 includes a plurality of inverters (not shown), and outputs a drivesignal via a corresponding one of the inverters to the first compressor11 a or the heat-source-side fan 19.

(4-4-2) First Expansion Valve Control Unit 56

The first expansion valve control unit 56 is a functional unit thatcontrols the opening degree of the first expansion valve 15. The firstexpansion valve control unit 56 controls, in real time, the openingdegree according to the control program and the set temperature, loadand the like of the service units 30 when none of the oil recoveryoperation first flag 516 and the oil recovery operation second flag 517are set (that is, when the control mode is in the normal mode).

When the oil recovery operation first flag 516 is set (that is, when thecontrol mode is the oil recovery control mode), the first expansionvalve control unit 56 executes the oil recovery first control. The oilrecovery first control is control for increasing the opening degree ofthe usage-side expansion valve 31. In the oil recovery first control,the first expansion valve control unit 56 set the opening degree of thefirst expansion valve 15 to a first opening degree.

The first opening degree is smaller than an opening degree of the firstexpansion valve 15 in the normal mode. When the first expansion valve 15is set to the first opening degree, the flow rate and the pressure of arefrigerant passing through the first expansion valve 15 reduce and theflow rate and the pressure of the refrigerant passing through the firstexpansion valve 15 and flowing into the service unit 30 reduce, wherebythe degree of superheating at the usage-side heat exchanger 32increases. In accordance therewith, the opening degree of the usage-sideexpansion valve 31 is increased. In the present embodiment, the firstopening degree is set to a minimum opening degree such that the openingdegree of the usage-side expansion valve 31 attains a maximum openingdegree by the oil recovery first control. In other words, the firstopening degree is an opening degree that causes the opening degree ofthe usage-side expansion valve 31 to be increased in relation to areduction in the flow rate or pressure of the refrigerant passingthrough the first expansion valve 15.

When the oil recovery operation second flag 517 is set (that is, whenthe oil recovery first control has been completed), the first expansionvalve control unit 56 executes the oil recovery second control. The oilrecovery second control is control for sending a liquid refrigerant forcompatibilizing with the refrigerating machine oil to the usage-sideheat exchanger 32. In the oil recovery second control, the firstexpansion valve control unit 56 sets the opening degree of the firstexpansion valve 15 to a second opening degree.

The second opening degree is greater than the opening degree of thefirst expansion valve 15 in the oil recovery first control. When thefirst expansion valve 15 is set to the second opening degree, the flowrate and the pressure of the refrigerant passing through the firstexpansion valve 15 increase and the flow rate and the pressure of therefrigerant passing through the first expansion valve 15 and flowinginto the service unit 30 increase, whereby the degree of superheating atthe usage-side heat exchanger 32 reduces. In accordance therewith, theopening degree of the usage-side expansion valve 31 is reduced.

Here, the opening degree of the usage-side expansion valve 31 changes bya delay corresponding to the response time, in response to the change inthe opening degree of the first expansion valve 15. That is, until thatresponse time elapses since when the first expansion valve 15 isswitched from the first opening degree to the second opening degree, theopening degree of the usage-side expansion valve 31 is maintained at theopening degree which has been increased by the oil recovery firstcontrol. Therefore, until the response time elapses since when the firstexpansion valve 15 is switched from the first opening degree to thesecond opening degree by the oil recovery second control, a liquidrefrigerant or a gas-liquid two-phase refrigerant having passed throughthe first expansion valve 15 is sent to the usage-side heat exchanger 32via the usage-side expansion valve 31. The liquid refrigerant or thegas-liquid two-phase refrigerant is compatibilized with a refrigeratingmachine oil built up in the usage-side heat exchanger 32, and flowstoward the gas side (the first pipe P1) of the heat source unit 10.Thus, the refrigerating machine oil built up in the usage-side heatexchanger 32 is recovered to the compressors 11.

In the present embodiment, the second opening degree of the firstexpansion valve 15 is set to the maximum opening degree so as tofacilitate sending the liquid refrigerant or the gas-liquid two-phaserefrigerant to the usage-side heat exchanger 32 by the oil recoverysecond control. It can be regarded that the second opening degree is anopening degree that allows, before the opening degree of the usage-sideexpansion valve 31 is reduced in relation to an increase in the flowrate or the pressure of the refrigerant passing through the firstexpansion valve 15, a liquid refrigerant to flow into the usage-sideheat exchanger 32 to be compatibilized with the refrigerating machineoil.

(5) Flow of Process at Controller 50

In the following, with reference to FIG. 3, a description will be givenof an exemplary flow of a process at the controller 50. FIG. 3 is aflowchart showing an exemplary flow of processes at the controller 50.

When the controller 50 is turned on and receives an operation startcommand, the controller 50 carries out processes according to the flowfrom steps S101 to S108 shown in FIG. 3. In FIG. 3, steps S102 to S106show a process relating to the oil recovery operation (the oil recoverycontrol mode). Steps S107 to S108 show a process relating to the coolingoperation (the normal mode). Note that, the process flow shown in FIG. 3is merely of an exemplary nature, and may be changed as appropriate. Forexample, the order of the steps may be changed unless a contradictionarises. Part of the steps may be executed in parallel to other steps.

In step S101, when the oil recovery operation start condition is notsatisfied (that is, when NO), the controller 50 proceeds to step S107.On the other hand, when the oil recovery operation start condition issatisfied (when YES), the controller 50 proceeds to step S102.

In step S102, the controller 50 enters the oil recovery control mode.Thereafter, the controller 50 proceeds to step S103.

In step S103, the controller 50 starts the oil recovery operation andexecutes the oil recovery first control. Specifically, the controller 50sets, as the oil recovery first control, the first expansion valve 15 tothe first opening degree. Thus, the flow rate and the pressure of arefrigerant passing through the first expansion valve 15 reduce and theflow rate and the pressure of the refrigerant having passed through thefirst expansion valve 15 and flowing into the service unit 30 reduce,whereby the degree of superheating at the usage-side heat exchanger 32increases. In accordance therewith, the opening degree of the usage-sideexpansion valve 31 is increased (in the present embodiment, the openingdegree is set to the maximum opening degree). Following the start ofexecuting the oil recovery first control, the controller 50 proceeds tostep S104.

In step S104, when the second control start condition is not satisfied(in the present embodiment, when the first time t1 has not elapsed sincethe start of executing the oil recovery first control, that is, whenNO), the controller 50 stays at step S104. On the other hand, when thesecond control start condition is satisfied (in the present embodiment,when the first time t1 has elapsed since the start of executing the oilrecovery first control, that is, when YES), the controller 50 proceedsto step S105.

In step S105, the controller 50 ends the oil recovery first control andexecutes the oil recovery second control. Specifically, the controller50 sets, as the oil recovery second control, the first expansion valve15 to the second opening degree. Thus, the flow rate and the pressure ofa refrigerant passing through the first expansion valve 15 increase andthe flow rate and the pressure of the refrigerant having passed throughthe first expansion valve 15 and flowing into the service unit 30increase, whereby the degree of superheating at the usage-side heatexchanger 32 reduces. In accordance therewith, the opening degree of theusage-side expansion valve 31 is reduced. Note that, until a responsetime elapses since when the first expansion valve 15 is switched fromthe first opening degree to the second opening degree, the openingdegree increased by the oil recovery first control (in the presentembodiment, the maximum opening degree) is maintained. Hence, until theresponse time elapses since when the first expansion valve 15 isswitched from the first opening degree to the second opening degree, aliquid refrigerant or a gas-liquid two-phase refrigerant passes throughthe first expansion valve 15, and the liquid refrigerant or thegas-liquid two-phase refrigerant flows into the usage-side heatexchanger 32. The liquid refrigerant or the gas-liquid two-phaserefrigerant flowing into the usage-side heat exchanger 32 iscompatibilized with a refrigerating machine oil built up in theusage-side heat exchanger 32, and flows toward the gas side (the firstpipe P1 and the second pipe P2) of the heat source unit 10. Thus, therefrigerating machine oil built up in the usage-side heat exchanger 32is recovered to the compressors 11. After the start of executing the oilrecovery second control, the controller 50 proceeds to step S106.

In step S106, when the oil recovery operation end condition is notsatisfied (in the present embodiment, when the second time t2 has notelapsed since the start of executing the oil recovery second control,that is, when NO), the controller 50 stays at step S106. On the otherhand, when the oil recovery operation end condition is satisfied (in thepresent embodiment, when the second time t2 has elapsed since the startof executing the oil recovery second control, that is, when YES), thecontroller 50 proceeds to step S107.

In step S107, the controller 50 enters the normal mode. Thereafter, thecontroller 50 proceeds to step S108.

In step S108, the controller 50 controls in real time the state of theactuators (11, 15, 16, 17, 19) in accordance with the set temperatureand the detected values of various types of sensors (20 to 23, 25) tocause them to perform the cooling operation. Thereafter, the controller50 returns to step S101.

(6) Oil Recovery Operation

As has been described above, the refrigeration apparatus 100 inoperation performs the oil recovery operation for recovering therefrigerating machine oil built up in the service units 30 to thecompressors 11 at a predetermined timing (specifically, at a timing whenthe oil recovery operation start condition is satisfied). In the oilrecovery operation, the controller 50 successively executes the oilrecovery first control and the oil recovery second control.

In the oil recovery first control, by the first expansion valve 15having its opening degree reduced to the first opening degree, the flowrate and the pressure of a refrigerant passing through the firstexpansion valve 15 (that is, a refrigerant sent to the service units 30)reduces. In relation thereto, the flow rate and the pressure of arefrigerant passing through the usage-side expansion valve 31 reduce andthe flow rate and the pressure of a refrigerant flowing into theusage-side heat exchanger 32 reduce. In accordance therewith, the degreeof superheating of the refrigerant at the usage-side heat exchanger 32increases. As a result, the opening degree of the usage-side expansionvalve 31 is increased.

In the oil recovery second control, by the first expansion valve 15having its opening degree increased to the second opening degree, theflow rate and the pressure of a refrigerant passing through the firstexpansion valve 15 increase. In relation thereto, the flow rate and thepressure of a refrigerant passing through the usage-side expansion valve31 increase and the flow rate and the pressure of a refrigerant flowinginto the usage-side heat exchanger 32 increase. In accordance therewith,the degree of superheating of the refrigerant at the usage-side heatexchanger 32 reduces. In response to the reduced degree, the openingdegree of the usage-side expansion valve 31 is reduced. Here, the timingat which the opening degree of the usage-side expansion valve 31 isreduced is delayed by a predetermined response time from the timingwhere the first expansion valve is set to the second opening degree.That is, there exists a time lag corresponding to the response time ofthe usage-side expansion valve 31 between the timing where the firstexpansion valve 15 is set to the second opening degree and the openingdegree of the usage-side expansion valve 31 is reduced.

Hence, during the period since when the first expansion valve 15 is setto the second opening degree until when the opening degree of theusage-side expansion valve 31 is reduced, the opening degree of theusage-side expansion valve 31 is maintained in the increased state bythe oil recovery first control. On the other hand, the flow rate of therefrigerant sent to the usage-side expansion valve 31 increases by thefirst expansion valve 15 is controlled to the second opening degree.Therefore, until the opening degree of the usage-side expansion valve 31is reduced, the liquid refrigerant flowed out from the receiver 13 issent to the usage-side heat exchanger 32. This liquid refrigeranttransfers the refrigerating machine oil built up in the usage-side heatexchanger 32 to the heat source unit 10, to be recovered to thecompressors 11.

In the refrigeration apparatus 100, executing the oil recovery operationincluding the oil recovery first control and the oil recovery secondcontrol recovers the refrigerating machine oil built up in theusage-side heat exchanger 32 to the compressors 11, without thenecessity of disposing an on-off valve on the refrigerant flow upstreamside relative to the usage-side expansion valve 31.

(7) Characteristic of Refrigeration Apparatus 100

(7-1)

The refrigeration apparatus 100 according to the above-describedembodiment is excellent in workability, maintainability, and economy.

That is, there exists a conventional refrigeration apparatus whichincludes an on-off valve disposed upstream to the mechanical expansionvalve. By the on-off valve being turned on or off, a liquid refrigerantis sent to the usage-side heat exchanger, to perform an oil recoveryoperation of recovering a refrigerating machine oil built up in theusage-side heat exchanger at a predetermined timing. In the case where acontroller for controlling, actuators is to be disposed outside theservice unit, such a conventional refrigeration apparatus necessitatesan electric wire for electrically connecting between the on-off valve inthe service unit and the controller in installation or maintenance. Forthe works relating to the electric wire, and troubles and costs inmaintenance, the conventional refrigeration apparatus is poor inworkability, maintainability, and economy.

In contrast, in the refrigeration apparatus 100, the controller 50executes the oil recovery operation for recovering the refrigeratingmachine oil to the compressors 11 at a predetermined timing. In the oilrecovery operation, the opening degree of the first expansion valve 15is set to the first opening degree, to reduce the flow rate and thepressure of a refrigerant passing through the first expansion valve 15.Thereafter, the opening degree of the first expansion valve 15 is set tothe second opening degree, to increase the flow rate and the pressure ofthe refrigerant passing through the first expansion valve 15. Thus, inthe oil recovery operation, under the oil recovery first control, inrelation to a reduction in the flow rate or the pressure of therefrigerant passing through the first expansion valve 15, the openingdegree of the usage-side expansion valve 31 is increased. Thereafter,under the oil recovery second control, before the opening degree of theusage-side expansion valve 31 is reduced in relation to the increase inthe flow rate or the pressure of the refrigerant passing through thefirst expansion valve 15, a liquid refrigerant flows into the usage-sideheat exchanger 32. As a result, the liquid refrigerant flowing into theusage-side heat exchanger 32 is compatibilized with a refrigeratingmachine oil building up in the usage-side heat exchanger 32 and flowstoward the heat source unit 10 side. Then, the refrigerating machine oilis recovered to the compressors 11.

That is, in the refrigeration apparatus 100, the oil recovery operationof recovering a refrigerating machine oil in the service units 30 to thecompressors 11 is carried out without the necessity of disposing anon-off valve for the oil recovery operation in the service units 30 (orin a refrigerant flow path downstream to the heat source unit 10 andupstream to the usage-side expansion valve 31; in the presentembodiment, the liquid-side connection pipe L1, the same holds true forthe following). In other words, in the refrigeration apparatus 100, therefrigerant circuit RC including the usage-side expansion valve 31upstream to the usage-side heat exchanger 32 performing the oil recoveryoperation does not require an on-off valve disposed upstream to theusage-side expansion valve 31. Hence, the refrigeration apparatus 100can dispense with an electric wire for electrically connecting betweenthe controller 50 and such an on-off valve in installation andmaintenance and, accordingly, the refrigeration apparatus 100 can saveany works relating to the electric wire and troubles and costs inmaintenance. Thus, the refrigeration apparatus 100 is excellent inworkability, maintainability, and economy.

(7-2)

In the refrigeration apparatus 100 according to the above-describedembodiment, the controller 50 first executes the oil recovery firstcontrol, and after a lapse of the first time t1, the controller 50executes the oil recovery second control. The first time t1 in theembodiment is a time that is required for the usage-side expansion valve31 to have its opening degree increased in response to a reduction inthe flow rate or the pressure of a refrigerant passing through the firstexpansion valve 15 by the oil recovery first control.

Thus, after the opening degree of the usage-side expansion valve 31 isincreased by the oil recovery first control being executed, the openingdegree of the first expansion valve 15 is increased by the oil recoverysecond control, whereby a liquid refrigerant by a flow rate suitable forrecovering a refrigerating machine oil flows into the usage-side heatexchanger 32. As a result, the oil recovery operation is realizedwithout the necessity of disposing an on-off valve for an oil recoveryoperation in the service units 30. Thus, any electric wire forelectrically connecting between the controller 50 and such an on-offvalve in installation or maintenance can be dispensed with and,accordingly, the refrigeration apparatus 100 can save any works relatingto the electric wire and troubles and costs in maintenance.

(7-3)

In the refrigeration apparatus 100 according to the above-describedembodiment, the usage-side expansion valve 31 includes the feeler bulb312 disposed on the refrigerant flow downstream side relative to theusage-side heat exchanger 32, and the opening degree of the usage-sideexpansion valve 31 is changed in response to the detected temperature bythe feeler bulb 312.

Thus, using the characteristic of the usage-side expansion valve 31including the feeler bulb 312, a liquid refrigerant is sent to theusage-side heat exchanger 32 to recover a refrigerating machine oil.That is, the opening degree of the usage-side expansion valve 31 is notimmediately changed in response to a change in the flow rate of arefrigerant sent from the upstream side (that is, a change in theopening degree of the first expansion valve 15). Instead, the openingdegree is changed by a delay corresponding to a response time inresponse to a change in the flow rate of a refrigerant sent from theupstream side. In other words, the usage-side expansion valve 31 ischaracterized by its low-speed responsivity. By virtue of thischaracteristic, when the oil recovery second control is executedfollowing the oil recovery first control, the opening degree of theusage-side expansion valve 31 is not immediately reduced. Hence, afterthe first expansion valve 15 is set to the second opening degree by theoil recovery second control and until the usage-side expansion valve 31has its opening degree reduced in response thereto, a liquid refrigerantis allowed to flow in by a flow rate suitable for recovering arefrigerating machine oil to the usage-side heat exchanger 32.

(7-4)

In the refrigeration apparatus 100 according to the above-describedembodiment, the first expansion valve 15 is disposed in the heat sourceunit 10. This eliminates the necessity of providing an electric wire forelectrically connecting between the heat source unit 10 and the serviceunit 30 disposed separate from each other. This particularly minimizesworks and costs relating to installation or maintenance.

(7-5)

In the refrigeration apparatus 100 according to the above-describedembodiment, the controller 50 is disposed at the heat source unit 10,and not electrically connected to any element disposed at the serviceunit 30. This eliminates the necessity of providing an electric wire forelectrically connecting between the heat source unit 10 and the serviceunit 30 disposed separate from each other. This particularly minimizesworks and costs relating to installation or maintenance.

(7-6)

In the refrigeration apparatus 100 according to the above-describedembodiment, the refrigerant circuit RC includes a plurality of serviceunits 30. That is, even in the case where a plurality of service units30 are installed (that is, in the case where electric wires are requiredfor electrically connecting between the heat source unit 10 and theservice units 30, which involves particularly complicated installationworks or maintenance works), the refrigeration apparatus 100 candispense with any electric wires required by an on-off valve for the oilrecovery operation installed in each of the service units 30. Thisparticularly minimizes works and costs relating to installation ormaintenance.

(8) Variations

The above-described embodiment can be modified as appropriate as shownin the following variations. Note that, the variations may be carriedout in combination with other variation unless any contradiction arises.

(8-1) Variation A

In the above-described embodiment, the second control start condition inthe oil recovery operation is satisfied by a lapse of the first time t1in the oil recovery first control. Note that, so long as the secondcontrol start condition is a condition which is satisfied by the openingdegree of the usage-side expansion valve 31 being increased in responseto the oil recovery first control, the second control start conditioncan be changed as appropriate in accordance with the designspecification or the installation environment. For example, the secondcontrol start condition may be satisfied by a detected value by any ofvarious types of sensors (21, 22, 23, or 25) attaining a predeterminedreference value (a value indicating an increase in the opening degree ofthe usage-side expansion valve 31) in the oil recovery first control.

(8-2) Variation B

In the above-described embodiment, the oil recovery operation endcondition in the oil recovery operation is satisfied by a lapse of thesecond time t2 in the oil recovery second control. Note that, so long asthe oil recovery operation end condition is a condition which issatisfied by the recovery of a refrigerating machine oil built up in theservice unit 30 (particularly, the usage-side heat exchanger 32) beingcompleted, the oil recovery operation end condition can be changed asappropriate in accordance with the design specification or theinstallation environment. For example, the oil recovery operation endcondition may be satisfied by a detected value by any of various typesof sensors (21, 22, 23, or 25) attaining a predetermined reference value(a value indicating the complete of recovery of a refrigerating machineoil built up in the service unit 30) in the oil recovery second control.

(8-3) Variation C

In the above-described embodiment, the first time t1 and the second timet2 are set to three minutes. Note that, the first time t1 and the secondtime t2 can be changed as appropriate in accordance with theinstallation environment and the design specification. For example, thefirst time t1 or the second time t2 may be set to a value less thanthree minutes (for example, one minute), or a value greater than threeminutes (for example, five minutes). Furthermore, the first time t1 andthe second time t2 may not be set to an identical value, and may berespectively set to different values.

(8-4) Variation D

In the above-described embodiment, the description has been given of theoil recovery first control under which the first expansion valve 15 hasits opening degree set to a minimum opening degree as the first openingdegree such that the usage-side expansion valve 31 has its openingdegree set to a maximum opening degree. Note that, the first openingdegree is just an opening degree smaller than an opening degree of thefirst expansion valve 15 in the normal mode, and may not be a minimumopening degree so long as it increases the opening degree of theusage-side expansion valve 31.

Further, in the oil recovery second control, the description has beengiven of the first expansion valve 15 having its opening degree set to amaximum opening degree as the second opening degree. Note that, thefirst opening degree is just an opening degree greater than the secondopening degree, and may not be a maximum opening degree so long as itallows a liquid refrigerant to flow into the usage-side heat exchanger32.

That is, so long as the object of the oil recovery first control and theoil recovery second control is achieved, the first opening degree andthe second opening degree should be set as appropriate in accordancewith the design specification and the installation environment.

(8-5) Variation E

In the above-described embodiment, the oil recovery operation isperformed when the oil recovery operation start condition is satisfiedin the cooling operation. Note that, the trigger of the oil recoveryoperation is not limited thereto, and may be changed as appropriate. Forexample, the oil recovery operation may be performed when the userinputs a predetermined command instructing the start of the oil recoveryoperation.

(8-6) Variation F

The configuration of the refrigerant circuit RC in the above-describedembodiment is not limited to the configuration shown in FIG. 1, and maybe changed as appropriate according, to the design specification and theinstallation environment.

For example, the first expansion valve 15 may not be disposed in theheat source unit 10. For example, the first expansion valve 15 may bedisposed at the liquid-side connection pipe L1.

For example, while three compressors 11 in total are disposed, thenumber of the compressors 11 may be changed as appropriate in accordancewith the design specification. For example, the compressors 11 may betwo in number, or four or more in number. In such cases, the number andallocation of the variable-capacity compressor and the constant-capacitycompressor should be selected as appropriate.

For example, the subcooling heat exchanger 14 and the injection line J1are not essential, and may be omitted as appropriate.

(8-7) Variation G

In the above-described embodiment, the usage-side expansion valve 31 isa thermostatic expansion valve including the feeler bulb 312. Note that,so long as the usage-side expansion valve 31 is an automatic regulatingvalve whose opening degree changes in response to a change in the flowrate or the pressure of the refrigerant sent from the upstream side, theusage-side expansion valve 31 may not be a thermostatic expansion valveand may be other mechanical expansion valve.

(8-8) Variation H

In the above-described embodiment, the usage-side fan 35 is notconnected to the controller 50. Note that, the usage-side fan 35 may beelectrically connected to the controller 50, and may have its start,stop or number of revolutions controlled by the controller 50. Theusage-side fan 35 may not be supplied with power from an independentpower source (a commercial power source, a storage battery or the like),and may be supplied with drive power from a power source unit sharedwith the heat source unit 10.

(8-9) Variation I

The above-described embodiment includes one heat source unit 10 and twoservice units 30. Note that, the number of the heat source unit 10disposed in the refrigeration apparatus 100 is not limited, and may betwo or more. The number of the service units 30 in the refrigerationapparatus 100 is not limited, and may be one, or three or more.

(8-10) Variation J

In the above-described embodiment, the controller 50 is disposed at theheat source unit 10. Note that, the controller 50 may not be disposed atthe heat source unit 10. For example, the controller 50 may be disposedat any unit other than the heat source unit 10, or may be disposedindependently. In such cases, the controller 50 may be disposed at aremote location connected to the heat source unit 10 via a communicationnetwork.

The configuration of the controller 50 is not limited to theconfiguration in the above-described embodiment, and may be changed asappropriate in accordance with the design specification or theinstallation environment. For example, the elements (the CPU, thememory, and various types of electric components) forming the controller50 may not be disposed at an identical position. The elements disposedin dispersed locations may be connected to each other via acommunication network to form the controller 50. That is, so long as theelements forming the controller 50 are configurable, the configurationof the controller 50 is not limited.

(8-11) Variation K

In the above-described embodiment, the present invention is applied tothe refrigeration apparatus 100 that cools a low-temperature warehouse,the inside of a showcase at a shop, or the usage-side space in thetransfer container. Without being limited thereto, the present inventionis applicable to other refrigeration apparatus including a refrigerantcircuit. For example, the present invention may be applied to an airconditioning system (an air conditioner) that realizes air conditioningby cooling the space inside a building.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a refrigeration apparatusincluding a refrigerant circuit.

REFERENCE SIGNS LIST

-   10: heat source unit-   11: compressor (actuator)-   12: heat-source-side heat exchanger-   13: receiver-   14: subcooling heat exchanger-   15: first expansion valve (electric valve, actuator)-   16: second expansion valve (actuator)-   17: injection valve-   19: heat-source-side fan (actuator)-   21: low-pressure side pressure sensor-   22: high-pressure side pressure sensor-   23: intermediate pressure sensor-   25: discharge temperature sensor-   30: service unit-   31: usage-side expansion valve (mechanical expansion valve)-   32: usage-side heat exchanger-   35: usage-side fan-   50: controller-   51: storage unit-   52: input control unit-   53: mode control unit-   54: actuator control unit-   55: drive signal output unit-   56: first expansion valve control unit-   100: refrigeration apparatus-   141: first flow path-   142: second flow path-   311: valve body-   312: feeler bulb-   313: capillary tube-   G1: gas-side connection pipe-   J1: injection line-   L1: liquid-side connection pipe-   P1 to P15: first pipe-fifteenth pipe-   RC: refrigerant circuit-   SV1: gas-side shutoff valve-   SV2: liquid-side shutoff valve-   t1: first time (predetermined time)-   t2: second time

CITATION LIST Patent Literature

-   Patent Literature 1: JP 2009-257759 A

1. A refrigeration apparatus configured to carry out a refrigerationcycle through a refrigerant circuit including: a heat source unitincluding a compressor configured to compress a refrigerant and aheat-source-side heat exchanger functioning as a condenser for therefrigerant; and a service unit including a usage-side heat exchangerfunctioning as an evaporator for the refrigerant, the refrigerationapparatus comprising: a mechanical expansion valve disposed on arefrigerant flow upstream side relative to the usage-side heat exchangerand configured to decompress a refrigerant passing through themechanical expansion valve in accordance with an opening degree of themechanical expansion valve; an electric valve disposed on therefrigerant flow upstream side relative to the mechanical expansionvalve and configured to adjust a flow rate or a pressure of arefrigerant passing through the electric valve in accordance with anopening degree of the electric valve; and a controller configured tocontrol an operation of a plurality of actuators, wherein the mechanicalexpansion valve has an opening degree changed in response to an increaseand a reduction in a flow rate or a pressure of a refrigerant flowingupstream to the mechanical expansion valve, the controller executes anoil recovery operation including a first control and a second controlfor recovering a refrigerating machine oil built up in the service unitto the compressor at a predetermined timing, by the first control, theelectric valve has an opening degree set to a predetermined firstopening degree to reduce the flow rate or the pressure of therefrigerant passing through the electric valve, by the second control,after the first control, the electric valve has an opening degree set toa second opening degree to increase the flow rate or the pressure of therefrigerant passing through the electric valve, the first opening degreeis an opening degree that causes the opening degree of the mechanicalexpansion valve to increase in relation to a reduction in the flow rateor the pressure of the refrigerant passing through the electric valve,and the second opening degree is an opening degree that allows, beforethe opening degree of the mechanical expansion valve is reduced inrelation to an increase in the flow rate or the pressure of therefrigerant passing through the electric valve, a liquid refrigerant toflow into the usage-side heat exchanger.
 2. The refrigeration apparatusaccording to claim 1, wherein the controller executes the first control,and executes the second control after a lapse of a predetermined timefrom execution of the first control.
 3. The refrigeration apparatusaccording to claim 1, wherein the mechanical expansion valve includes afeeler bulb disposed on a refrigerant flow downstream side relative tothe usage-side heat exchanger, and has an opening degree changed inresponse to a detected temperature by the feeler bulb.
 4. Therefrigeration apparatus according to claim 1, wherein the electric valveis disposed in the heat source unit.
 5. The refrigeration apparatusaccording to claim 1, wherein the controller is disposed at the heatsource unit and not electrically connected to any element disposed atthe service unit.
 6. The refrigeration apparatus according to claim 1,wherein the refrigerant circuit includes a plurality of the serviceunits.
 7. The refrigeration apparatus according to claim 2, wherein themechanical expansion valve includes a feeler bulb disposed on arefrigerant flow downstream side relative to the usage-side heatexchanger, and has an opening degree changed in response to a detectedtemperature by the feeler bulb.
 8. The refrigeration apparatus accordingto claim 2, wherein the electric valve is disposed in the heat sourceunit.
 9. The refrigeration apparatus according to claim 3, wherein theelectric valve is disposed in the heat source unit.
 10. Therefrigeration apparatus according to claim 2, wherein the controller isdisposed at the heat source unit and not electrically connected to anyelement disposed at the service unit.
 11. The refrigeration apparatusaccording to claim 3, wherein the controller is disposed at the heatsource unit and not electrically connected to any element disposed atthe service unit.
 12. The refrigeration apparatus according to claim 4,wherein the controller is disposed at the heat source unit and notelectrically connected to any element disposed at the service unit. 13.The refrigeration apparatus according to claim 2, wherein therefrigerant circuit includes a plurality of the service units.
 14. Therefrigeration apparatus according to claim 3, wherein the refrigerantcircuit includes a plurality of the service units.
 15. The refrigerationapparatus according to claim 4, wherein the refrigerant circuit includesa plurality of the service units.
 16. The refrigeration apparatusaccording to claim 5, wherein the refrigerant circuit includes aplurality of the service units.